As environmentally friendly vehicles, hybrid vehicles have been developed and put into practical use. Each of the hybrid vehicles includes: a motor for generating vehicle driving power; a power storage device for storing electric power for driving the motor; and an internal combustion engine. Further, output of the internal combustion engine is used as the vehicle driving power and/or motive power for generating electric power to charge the power storage device. Such a conventional hybrid vehicle generally performs charging/discharging control to maintain an SOC (State Of Charge) at a 50-60% level of the fully charged state, in order to secure electric power for generating driving power by the motor while permitting reception of regenerative power upon regenerative braking. The SOC is indicative of a remaining level of the power storage device.
Particularly, in recent years, it has been proposed to charge a vehicular power storage device of such a hybrid vehicle using a power source external to the vehicle (hereinafter, also referred to as “external power source”). In the hybrid vehicle chargeable by the external power source such as a plug-in type hybrid vehicle, for improved energy efficiency, charging/discharging control is oriented to externally charging the power storage device to the fully charged state level before starting traveling and to consuming the electric power in the power storage device up to a value near an SOC management lower limit value when ending the traveling.
Further, for example, Japanese Patent Laying-Open No. 2003-209969 (PTL 1) and Japanese Patent Laying-Open No. 2008-109840 (PTL 2) describe that a plurality of power storage devices (batteries) are connected to one another in parallel in order to achieve a longer traveling distance using electric power stored in the vehicular power storage devices.
PTL 1 describes a power source system controlled by equalizing charging/discharging of each of the power storage devices by arranging converters respectively corresponding to the plurality of power storage devices arranged in parallel. PTL 2 describes that charging/discharging control is performed in accordance with a distribution ratio of charging/discharging electric power among the plurality of power storage devices. The distribution ratio is sequentially calculated in accordance with a ratio of permitted charging/discharging levels among the power storage devices. In this way, even when the plurality of power storage devices have different charging/discharging properties, the system can exhibit its maximum performance.
PTL 1: Japanese Patent Laying-Open No. 2003-209969
PTL 2: Japanese Patent Laying-Open No. 2008-109840